Borehole seismic surveys are among downhole measurements used in the hydrocarbon industry. Originally, borehole seismic surveys were limited to correlating time-based surface seismic images with depth-based well logs and depth-based reservoir models for the purpose of making drilling decisions. Modern borehole seismic applications, however, extend beyond simple time-depth correlations to generate a variety of useful information about reservoir extent, geometry and heterogeneity, as well as fluid content and pore-pressure, rock mechanical properties, enhanced oil-recovery progress, elastic anisotropy parameters, induced fractures geometry and natural fracture orientation and intensity. Borehole seismic measurements have also extended beyond applications in the hydrocarbon industry to include applications in the hydrology and subterranean carbon sequestration industries.
Regardless of the application, deployment of seismic survey tools in wellbores may be constrained by cost and physical size considerations. For instance, in the hydrocarbon production industry, borehole seismic survey tools may have a diameter of two or more inches and, thus, cannot physically fit in a wellbore if either a drillstring or tubing is in place (unless detectors are placed on the drillstring before drilling is commenced). As a result, the performance of a borehole seismic survey may entail pulling the drillstring or production tubing (if one or the other is in place), running an array of survey tools into the wellbore, conducting the survey, pulling the tool array, and then replacing the drillstring or tubing (if needed). For this reason, a seismic survey may be costly, both in terms of rig time and, in some instances, lost production while the survey is being performed.
Borehole survey tools used as described above can include downhole sensors and electronics. The harsh downhole environment increases the complexity and cost of the sensors and electronics designed to withstand elevated temperatures and pressures for extended periods of time. Consequently, seismic survey tools generally are not treated as disposable, and may not be either abandoned in the wellbore after use or left inactive in a wellbore for extended periods (such as for time-lapse surveys) due to lost revenues that could be obtained by deploying the survey tools in other locations.